In recent years, the use of various electric vehicles has been promoted with the expectation of solving environmental/energy issues. Secondary batteries are being developed intensively as a vehicle-mounted power source, such as a motor drive power source, which holds the key to the practical application of these electric vehicles. However, in order to ensure widespread use, it is necessary to increase the performance and reduce the cost of batteries. In addition, with an electric vehicle, it is necessary to bring the single-charge driving range closer to that of a gasoline engine vehicle and batteries with higher energy are in demand.
In order for batteries to have a high energy density, it is necessary to reduce as much as possible battery members that are not directly related to a battery reaction. As a battery which allows saving of current collecting tab of a battery single cell or bus bar for connection between single cells, has very high volume efficiency, and is suitable for mounting in vehicles, a bipolar type secondary battery has been suggested. In a bipolar type secondary battery, a bipolar type electrode in which a positive electrode is formed on one surface of a single current collector and a negative electrode is formed on the other surface of the same current collector is used. Furthermore, it has a structure in which plural bipolar type electrodes are laminated such that the positive electrode and negative electrode can face each other having a separator containing an electrolyte layer interposed therebetween. Accordingly, the bipolar type secondary battery forms one battery cell (i.e., single battery) consisting of a current collector, a positive electrode and a negative electrode, and a separator (i.e., electrolyte layer) present between current collectors.
Furthermore, for the purpose improving the output density per weight of a bipolar type secondary battery, use of a current collector (so-called resin current collector) containing polyolefin resin (polymer material) and carbon-based conductive filler is suggested in Patent Literature 1. Namely, it is described that the output density per weight of a secondary battery can be increased because this resin current collector has less weight than a metal foil current collector.